Furnace wall comprising feed nozzles molded in two complementary parts

ABSTRACT

A fluid, especially secondary air, feed nozzle of an incinerator furnace, in accordance with the invention, is made in two complementary recessed parts (11, 12). These parts are molded from refractory material (silicon carbide, for example) and assembled by pressing so as to have an outside shape identical to that of the bricks which constitute the wall of the furnace.

The present invention concerns a furnace wall, especially of anincinerator, comprising secondary air feed nozzles.

As a general rule the walls of incinerators, especially those forburning urban waste, comprise secondary air feed nozzles.

These walls generally contain a bundle of tubes for heating watercirculating within them for subsequent recovery of the thermal energythus obtained. The nozzles, which pass through the wall, are thusnecessarily inserted between neighbouring pipes to feed secondary airinto the furnace from feed means.

The walls are generally of refractory materials, specifically in theform of bricks, which are not subject to corrosion. It is known thatburning waste produces sulfides (especially CaS, Na2S and FeS) whichmake the environment inside the furnace especially corrosive.

The secondary air feed nozzles usually project from the inside wall ofthe furnace. The disadvantage of this is that the projecting part isexposed to the corrosive action of the air laden with sulfides insidethe furnace.

This major disadvantage has been overcome in part by surrounding theprojecting parts of the nozzles with cement so that only the nozzleopening is exposed. Nevertheless, the inside wall of the nozzle remainsin contact with the corrosive air inside the furnace through thisopening. Also, ash and waste materials volatilized during combustiontend to collect on the projecting parts. They are rich in sulfides asthey have not been completely combusted. This creates two problems whichtend to aggravate each other: on the one hand, the sulfides collectingin this way on the projecting parts are even more corrosive than thesurrounding environment; on the other hand, they tend to clog the nozzleoutlets and so to worsen combustion conditions by reducing the input ofsecondary air. As is well known, incomplete combustion increases theconcentration of sulfides, which are reduced to solid sulfates only oncomplete combustion. There therefore results a self-perpetuatingphenomenon resulting in fouling and corrosion of the furnace, and theremay be no remedy for such corrosion.

It is, of course, possible to shut down the furnace periodically inorder to clean it and where necessary replace any excessively corrodedparts, but this has obvious major disadvantages which are betteravoided.

The object of the present invention is to circumvent the disadvantagesmentioned hereinabove by proposing, in accordance with the invention, afurnace wall, in particular an incinerator furnace wall, of the kindconstructed of elements assembled in the manner of bricks of whichcertain elements are hollow and constitute nozzles for feeding secondaryair into the furnace, said elements being disposed around pipes adaptedto convey a cooling fluid, the pipes being disposed in bundles andconstituting a metal framework for the wall, characterized in that eachnozzle-forming element is in two parts each formed with a longitudinalrecess mated together at a substantially horizontal jointing surface andin that the nozzles discharge into the furnace through a generally planeface of the element continuously merging with the corresponding faces ofthe adjacent elements.

This makes it possible to construct a furnace the walls of which aresmooth and offer no opportunity for waste materials, especiallysulfides, to accumulate. Moreover, in this way the use of metal, whichis subject to corrosion, is avoided through the use of the longitudinalrecesses in the two parts which are made of a refractory material, suchas silicon carbide, for example.

Also, such nozzles are particularly simple and economical tomanufacture, as the refractory material is easily molded.

The characteristics and advantages of the invention will emerge from thefollowing description given by way of example with reference to theappended drawings, in which:

FIG. 1 shows in longitudinal cross-section an element forming a nozzlein accordance with the invention;

FIG. 2 shows in plan view an element forming a nozzle in accordance withthe invention;

FIG. 3 shows in transverse cross-section an element forming a nozzle inaccordance with the invention;

FIG. 4 is a view in elevation of the anterior surface of an elementforming a nozzle in accordance with the invention;

FIG. 5 shows in elevation and in perspective an element forming a nozzlein accordance with the invention cut longitudinally on a vertical plane;and

FIG. 6 shows in elevation and in perspective a furnace wall comprisingnozzles in accordance with the invention.

A secondary air feed nozzle of a furnace specifically designed forincineration of waste and constituting one preferred embodiment of theinvention is shown in FIGS. 1 through 5.

A nozzle in accordance with the invention comprises two superposedparts, an upper part 11 and a lower part 12. These parts are matedtogether at a so-called jointing surface 17 extending longitudinally andsubstantially horizontally, that is to say normally to the lateralsurfaces of the element 10 obtained by superposing the upper and lowerparts 11 and 12. The two parts 11 and 12 have longitudinal recesses witha shape which, when the two parts are placed together, forms a hollownozzle within the element 10. The recesses formed in the upper and lowerparts 11 and 12 are such that the jointing surface 17 is substantiallyin the middle of the resulting nozzle.

The element 10 has an anterior part and a posterior part, the anteriorpart being at the same end as the mouth of the nozzle 13 and theposterior part being at the other end, to which the secondary air feedmeans are connected. These secondary air feed means, which are known inthemselves, do not constitute an integral part of the invention and arenot shown in the drawings. On the posterior side of the element 10 thenozzle has a first part 14 of generally cylindrical cross-section formedwith two annular grooves 21 running concentrically around it. This part14 is designed to accommodate a projecting part of the secondary airfeed means inserted into the part 14 of the nozzle. The projecting partof the feed means, the part 14 of the nozzle and the annular grooves 21form connecting means between the nozzle and the secondary air feedmeans.

After the part 14 the nozzle features a cylindrical intermediate part 15the diameter of which is less than that of the part 14.

An anterior part of the nozzle 16, generally of flattened beak shape,connects the end of the part 15 to the mouth of the nozzle 13. The uppercontour 20 of the part 16 shown in the longitudinal cross-section(FIG. 1) comprises a first segment which extends in a linear manner theupper contour of the cylindrical part 15 and then, substantially in linewith the middle of the part 16, curves to define a circular arc which isthen extended by a rectilinear end segment as far as the mouth of thenozzle 13. The contour 20 is downwardly inclined, with the result thatthe longitudinal thickness of the upper part 11 of the element 10 isgreater at the level of the mouth 13 than at the level of the junctionbetween the parts 15 and 16.

The lower contour 19 of the anterior part 16 of the nozzle rises andconverges from the junction with the part 15 towards the contour 20 asfar as the middle longitudinal level of the anterior part 16 where thecontour 20 is curved. In this middle area of the anterior part 16 thecontour 19 is also curved to define a circular arc which is thenextended downwardly by a straight line segment as far as the mouth 13.Nevertheless, the inclination of the rectilinear segment of the contour19 nearest the mouth 13 is less than that of the corresponding segmentof the contour 20. Thus over all of the anterior part 16 of the nozzleand up to the mouth 13 the contours 19 and 20 tend to converge,corresponding to a reduction in the longitudinal cross-section of thenozzle in this part. In the anterior part 16 of the nozzle the contour19 is substantially symmetrical relative to a line perpendicular to thelower surface of the part 12 of the element 10 and median to theanterior part 16 of the nozzle.

The joint surface 17 extends substantially horizontally andlongitudinally in a middle position of the nozzle; it is curved in theanterior part 16 of the nozzle, remaining substantially halfway betweentwo contours 19 and 20.

As shown in FIG. 2, the cross-section of the nozzle in the joint surface17 forms an isosceles trapezium in the anterior part 16. Thiscorresponds to a widening of the nozzle from the junction between theintermediate part 15 and the anterior part 16 up to the mouth 13 of thenozzle. The mouth 13 of the nozzle is an opening coplanar with theanterior surface of the element 10. As shown in FIG. 4, this mouth 13 isgenerally hippodrome-shaped, having a substantially rectangular shapewith semi-circles on the two shorter sides, as shown in FIG. 4. Thejoint surface 17 which passes through the middle of the mouth 13 has oneither side of the mouth two symmetrical cranks 18 the transversecross-sections of which are generally trapezoidal.

As shown in FIG. 2, the parts 11 and 12 forming the nozzle comprise twolateral recesses 22 the general shape of which is part-cylindrical andwhich extend symmetrically to each side of the longitudinal axis of theelement 10 and normal to the joint surface 17. In this embodiment of theinvention the anterior part of the element 10 in front of the lateralrecesses is wider than the posterior part to the rear of the lateralrecesses 22. As shown in FIGS. 2 and 3, the lateral recesses 22 areflared, one in the upper part 11 and the other in the lower part 12, toform half-funnel shapes respectively towards the top and the bottom ofthe element 10.

Because of the separation of the two longitudinal cranks 18, they areintersected by the lateral recesses 22. Note that in the embodiment ofthe invention described, the longitudinal cranks 18 are separated intotwo parts, an anterior part and a posterior part, by the lateralrecesses and are disposed relative to the lateral edges of the element10 so that each anterior part of a crank 18 is not in alignment with itsposterior part.

More precisely, the distance that separates each crank 18 from thenearest lateral edge remains substantially constant over all the lengthof the element 10.

As shown in FIG. 6, a furnace wall 17 in accordance with the invention,part of a furnace for incinerating waste, for example, is made up ofelements 10 and 26 of refractory material and all of identical overalldimensions. A bundle of cylindrical and parallel pipes 24 passes betweenthese elements in the openings 22 formed therein, such pipesadvantageously providing for circulation of water to be heated bycontact with the bricks. In practice, thermal interchange simultaneouslycools the wall, preventing its temperature rising excessively, and heatsthe circulating water so that energy is thereby recovered.

The bundle of pipes 24 thus formed is substantially parallel to theanterior surface of the wall 27 of the furnace comprising the combinedanterior surfaces of the elements 10 and the elements 26 of identicalshape and size. In practice a bundle of pipes of this kind forms a metalframework for the furnace wall.

In practice the pipes 24 are the water tubes of a boiler.

The elements 10 and the elements 26 are stacked up in the manner ofbricks, in consecutive adjacent stacks joined together by joints 25. Thejoints 25 link the anterior lateral surfaces of adjacent elements 10 and26, these surfaces being in front of the pipes 24. As the posteriorwidth of the elements 26 and 10 behind the bundle of pipes 24 is lessthan the anterior width, the stacks of elements 10 and 26 are notlaterally contiguous over all their depth. This is not of anysignificant importance, as the anterior parts serve only to hold theelements 26 and 10 in place by preventing any longitudinal displacementof each element relative to the bundle of pipes 24 which thus immobilizeit. Note that by distributing a certain number of elements 10 in thefurnace wall it is possible to provide the appropriate number of nozzlesat the appropriate locations without creating any discontinuity in thesurface of the furnace wall. It is thus possible to introduce a smallnumber of elements 10 in place of elements 26, in practice bricks, andto dispose them at the appropriate locations without any disadvantageregarding the construction of the wall 27. The elements 10 and 26 areplaced identically by virtue of the half-funnel flared shapes of thelateral recesses 22 in these elements which enable them to be initiallydisposed slantwise between two adjacent pipes 24 and then fitted intoplace with a simple tilting movement.

It is advantageous to make the furnace wall of silicon carbide. The useof this material favours thermal interchange between the wall and thebundle of pipes.

It is possible in accordance with the invention to make the nozzles intwo parts 11 and 12 as described hereinabove, each of these parts beingmolded in the same material as the refractory bricks 26, which issilicon carbide in this instance. A nozzle in accordance with theinvention is obtained by simply pressing into superposition at the jointsurface 17 the lower and upper parts 12 and 11 of an element 10 inaccordance with the invention. The longitudinal cranks 18 in the jointsurface 17 permit precise juxtaposition of the upper and lower parts 11and 12 of the element 10. It is possible, in a preferred embodiment ofthe invention, to provide cranks 18 at the joint surface 17 which areslightly deeper in the part comprising the recessed crank, the upperpart in the example shown, than the projecting crank, here in the lowerpart. This makes it possible to place in the space thus left at thebottom of these cranks a fixing seal, in the form of cement, forexample. A fixing seal of this kind makes it possible to fasten theparts 11 and 12 of the element 10 together in a non-removable manner.The element 10 that results is then as if of unitary construction andcan be handled as such and form an integral part of the furnace wall, inthe same way as a brick 26, whilst still including a secondary air feednozzle that does not have any projection on the front surface and thatdoes not comprise any metal part. Silicon carbide is chosen as therefractory material in the preferred embodiment of the invention, butthose skilled in the art can instead choose any other appropriaterefractory material. Likewise, the shape of the nozzle may be adapted tothe specific requirements of the embodiment selected by those skilled inthe art, and similarly the means for connected the nozzle to thesecondary air feed means may be different. It may also be possible toenvisage other ways of mounting the elements between adjacent pipes of abundle of pipes, which are not necessarily vertical. It may also befeasible to make the elements 10 in accordance with the invention in twoparts mated together at a vertical longitudinal joint plane,substantially parallel to the lateral walls of the element. Thecentering cranks on the joint plane may equally well be replaced byother devices, for example male and female locators or any other devicechosen by those skilled in the art. Generally speaking, the invention isnot limited to the preferred embodiment described but encompasses allvariations and improvements that may be made thereto by those skilled inthe art.

I claim:
 1. A furnace wall, in particular an incinerator furnace wall, of the kind constructed of elements (10, 26) assembled in the manner of bricks some of said elements (10) being hollow nozzle-forming elements for feeding secondary air into the furnace, said elements being disposed around pipes (24) adapted to convey a cooling fluid, the pipes being disposed in bundles and constituting a metal framework for the wall, characterized in that each of said nozzle-forming elements is in two parts (11, 12), each of the parts having a longitudinal recess mating with the other of the parts along a substantially horizontal jointing surface (17), and each of each nozzle-forming elements having a discharge into the furnace through a generally plane face of the element (10) contiguous with the corresponding faces of the adjacent ones of said elements (26).
 2. A furnace wall according to claim 1, characterized in that the pipes (24) are disposed in bundles and are entirely embedded within the wall so as to be isolated from the interior of the furnace.
 3. A furnace wall according to claim 1, characterized in that the elements (10, 26) constituting the wall are made of silicon carbide.
 4. A furnace wall according to claim 1, characterized in that the pipes (24) are the water tubes of a boiler adapted to receive thermal energy through contact with elements (10, 26) of the wall.
 5. A furnace wall according to claim 1, characterized in that each of said elements (10, 26) comprises two substantially vertical lateral recesses (22) flared to a substantially half-funnel shape symmetrically relative to the longitudinal axis of the element, so as to enable said elements to be fitted between adjacent pipes (24) by tilting them axially.
 6. A furnace wall according to claim 1, characterized in that each nozzle-forming element has at least one arcuate part to prevent any longitudinal displacement of one part of the element relative to the other.
 7. A furnace wall according to claim 1, characterized in that the jointing surface (17) of the two parts of each of said nozzle-formingelements (10) includes two longitudinal splines (18) arranged one on each side of the recesses therein, adapted to prevent any lateral translation of one part relative to the other.
 8. A furnace wall according to claim 7, characterized in that said longitudinal splines (18) have a trapezoidal cross-section. 